Mt. Gox, once the world’s largest bitcoin exchange, has gone offline, apparently after losing hundreds of millions of dollars due to a years-long hacking effort that went unnoticed by the company.

The hacking attack is detailed in a leaked “crisis strategy draft” plan, apparently created by Gox and published Monday by Ryan Selkis, a bitcoin entrepreneur and blogger (see below). According to the document, the exchange is insolvent after losing 744,408 bitcoins — worth about $350 million at Monday’s trading prices. The plan paints a bleak picture of the exchange’s finances and outlines an arbitrage scheme to restore the exchange to solvency. “The reality is that Mt. Gox can go bankrupt at any moment, and certainly deserves to as a company,” the document states.